The invention relates to a vehicle having an electrical drive machine, comprising a braking device and a gear selecting device.
Hybrid and electric vehicles have an electrical driving machine. Frequently, permanently excited synchronous machines are used for this purpose. In the case of permanently excited synchronous machines, permanent magnets are used for the rotor, which permanent magnets generate a magnetic field without an external excitation, which magnetic field generates a torque on the rotor axis in an interaction with a 3-phase excitation of the stator. This torque can be collected from the rotor axis for the purpose of the traction of the vehicle. The traction of the vehicle can be controlled by way of a braking device, a gear selecting device and an accelerator pedal of the vehicle. This is illustrated, for example, in European Patent Document EP 0 096 468 A2.
It is an object of the invention to describe an improved vehicle having an electrical drive machine, comprising a braking device and a gear selecting device.
According to the invention, the electrical machine is designed as a current-excited synchronous machine. The vehicle has a control unit which is assigned to the current-excited synchronous machine. The control unit sets an exciting current of the rotor. The setting of the exciting current takes place as a function of a gear selecting position set at the gear selecting device, and the setting of the exciting current takes place takes place as a function of a position of the brake pedal of the braking device.
This means that the setting of the exciting current of the current-excited synchronous machine is a function of the setting at the gear selecting device as well as of the position of the brake pedal.
According to a preferred embodiment, it is particularly advantageous for the gear selecting device to have a first adjustable gear selecting position for parking the vehicle, for the gear selecting device to have a second adjustable gear selecting position for a frictional uncoupling of the wheels of the vehicle, for the gear selecting device to have a third adjustable gear selecting position for a driving operation of the vehicle when traveling forward, for the gear selecting device to have a fourth adjustable gear selecting position for a driving operation of the vehicle when traveling backward, and information can be transmitted to the control unit by way of the set gear selecting position.
In the following, the first adjustable gear selecting position will also be called “Parking”; the second adjustable gear selecting position will also be called “Neutral”; the third adjustable gear selecting position will be called “Drive”; and the fourth adjustable gear selecting position will be called “Reverse”.
The gear selecting device therefore makes it possible for a user of the vehicle to select a driving mode whose function can be compared with the function of a transmission in the case of a conventional vehicle.
According to a further variant of the invention, the vehicle comprises a measuring device which determines a relative position of the brake pedal with respect to a predefined brake pedal travel, which brake pedal travel is defined by a minimal brake pedal value and by a maximal brake pedal value. The determined relative position of the brake pedal can be transmitted to the control unit.
It is particularly advantageous for the control unit to switch off the exciting current in the “Parking” gear selecting position and in the “Neutral” gear selecting position.
This means that the rotor magnetic field is de-energized in the “Parking” gear selecting position and in the “Neutral” gear selecting position. In these gear selecting positions, a traction of the vehicle, i.e. a driving operation, is not intended. The current-excitation of the rotor may therefore be deactivated.
In addition, special advantages are obtained when, in the “Drive” gear selecting position and at a brake pedal value between the maximal brake pedal value and a first critical brake pedal value, the control unit switches off the exciting current, and, in the “Reverse” gear selecting position and at a brake pedal value between the maximal brake pedal value and the first critical brake pedal value, the control unit switches off the exciting current.
In this manner, it is ensured that the exciting current is switched off according to the demand. If the brake pedal value exceeds the first critical value on the way of the maximal brake pedal value, the exciting current of the synchronous machine will be switched off.
In a further variant of the invention, in the “Drive” gear selecting position and at a brake pedal value between the minimal brake pedal value and a second critical brake pedal value, the control unit will set the exciting current. The control unit further sets the exciting current in the “Reverse” gear selecting position and at a brake pedal value between the minimal brake pedal value and the second critical brake pedal value.
If the brake pedal value exceeds a second critical value in the direction of the minimal brake pedal value, the exciting current of the synchronous machine will be set. It is thereby ensured that the exciting circuit of the synchronous machine is activated in the case of a low braking power or braking force and a traction toque can be demanded from the synchronous machine at any time.
The invention is based on the following considerations:
For reasons of energy and power efficiency, permanently excited synchronous machines are widely applied in electric and hybrid vehicles. In this type of machine, the rotor is permanently excited because permanent magnets are used for generating magnetic fields.
As an alternative, current-excited synchronous machines can be used which have no magnetic materials in the rotor. Instead, an exciting magnetic field is electromagnetically generated by copper windings. The current generating this magnetic field can be strategically controlled with respect to the operation; i.e. in contrast to a permanently excited machine, this exciting current forms an additional degree of freedom during the operation of the machine.
This means that the torque generated at the electrical machine is not only a function of a torque-forming current and a field-forming current but also of the exciting current.
Normally, exciting windings have a high inductivity and a low ohmic resistance. This results in a high time constant, which is proportional to the inductivity and indirectly proportional to the ohmic resistance. It is therefore a challenging task to provide operating strategies for a torque demand with very high time-related dynamics.
By means of the following embodiment of the invention, an operating strategy is described which permits a dynamic torque demand to a current-excited synchronous machine in a hybrid or electric vehicle and compensates the relatively sluggish dynamics of the exciting magnetic field.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
Further details, preferred embodiments and further developments are obtained from the above.